Different conductor structures are used in the structures of electronic devices. The higher the frequencies used in the devices, the greater the requirements set for the conductor structures used, so that the attenuation caused by the conductor structures does not become too high or that the conductor structure used does not disturb other parts of the apparatus by radiation. The designer of the device can select from many possible conductor structures. Depending on the application, an air-filled waveguide made of metal, for example, can be used. The basic structure, dimensions, and waveforms that can propagate in the waveguide and the frequency properties of the waveguide are well known (see e.g. chapter 8 Fields and Waves in Communication Electronics, Simon Ramo et al., John Wiley & Sons, inc., USA). FIG. 1 shows, as an example of the dimensioning of a waveguide, a rectangular waveguide made of conductive material, the width of which is a in the direction of the x-axis of the coordinates shown in the figure, the height of which is b in the direction of the y-axis, and which is filled by air, whose permittivity εr is of magnitude 1. In the air-filled waveguide shown in FIG. 1, the first (lowest) waveform that can propagate in the direction of the z-axis is the so-called TE10(Transverse-electric) waveform. The electric field E of this waveform does not have a component in the direction of the z-axis at all. Instead, the magnetic field H has a component in the direction of propagation, the direction of the z-axis. The so-called cut-off frequency fc of the waveform TE10, which means the lowest frequency that can propagate in the waveguide, is obtained from the equation:       f          cTE      10        =      c          2      ⁢      a      where the letter a means the width a of the waveguide in the direction of the x-axis, and c is the speed of light in a vacuum. Generally, the usable frequency range of the waveguide is 1.2 to 1.9 times the cut-off frequency of the waveform in question. The usable lower limiting frequency is determined by the growth of the attenuation when the cut-off frequency fc is approached from above. The upper frequency limit again is determined by the fact that with frequencies that are more than twice the cut-off frequency fc of the desired waveform, other waveforms that are capable of propagating are also created in the waveguide, and this should be avoided.
There are also known waveguide structures, in which the waveguide is formed by a core part made of dielectric material, which is coated with a thin layer of conductive material. However, these waveguides are always made as separate components. The above described waveguide structures provide a small attenuation per unit of length, and they do not emit much interference radiation to the environment. However, the problem with these waveguides is the large physical size compared to the rest of the circuit unit to be manufactured, and the fact that it is difficult to integrate their manufacture into the manufacture of the circuit unit as a whole. These waveguides must be joined to the circuit unit mechanically either by soldering or by some other mechanical joint in a separate step, which increases costs and the risk of failure.
Conductor structures that are better integrated into the structure are also utilized in electronic equipment. These include strip lines, microstrips and coplanar conductors. Their manufacture can be integrated into the manufacture of the circuit unit as a whole, when circuit units are manufactured as ceramic structures. This manufacturing technique is called multilayer ceramics, and it is based either on the HTCC (High Temperature Cofired Ceramics) or LTCC (Low Temperature Cofired Ceramics) technique. The circuit structures implemented with either of these manufacturing techniques consist of multiple layers of ceramic material (green tape), which are 100 μm thick and placed on top of each other when the circuit structure is assembled. Before the heat treatment, which is performed as the final treatment, the ceramic material is still soft, and thus it is possible to make cavities and vias of the desired shape in the ceramic layers. It is also possible to make various electrically passive elements and the above-mentioned conductors on the desired points with silk screen printing. When the desired circuit unit is structurally complete, the ceramic multilayer structure is fired in a suitable temperature. The temperature used in the LTCC technique is around 850° C. and in the HTCC technique around 1600° C. However, the problem of microstrips, strip lines and coplanar conductors made with these techniques is the high attenuation per unit of length, low power margin and relatively low ElectroMagnetic Compatibility (EMC). These problems limit the use of these conductor structures in the applications where the above-mentioned properties are needed.